Burners for gaseous fuels are generally divided into fan-assisted burners and atmospheric burners.
In general, in using atmospheric burners an imperfect combustion may occur, with harmful emissions of carbon monoxide and nitric oxides which can cause atmospheric pollution.
EP-A-0009831 refers to an atmospheric burner (POLIDORO) in which the perforated surface of a cylindrical burner diffuser consists of transverse groups comprising subgroups of slots spaced out 2 mm in a transverse direction, with pilot holes at each end. Each sub-group consists of a densely-packed series of parallel transverse slot with center distance of only 1.2 mm, in order to obtain a "single flame front" from each group, i.e., a big vertical flame, with the aim of reducing burner noise and providing high thermal power.
Also known, per EP-A-0217470, is an atmospheric burner (NEFIT) in which the primary air-gas mixture, drawn in through a Venturi tube, is then directed downwards at the outlet of this tube. The flow is then fed back, up at the side with turbulence reduced to a minimum, to feed the slots in a perforated diffuser. The purpose is to obtain combustion which is as uniform as possible, "without any disturbing noise being produced". In fact (see figures) the surfaces of the diffuser of the body present groups of slots similar to EP-A-0009831.
Also, DE-A-2132968 (FOGLIANI, PANINI and VECCHI), teaches covering of an atmospheric burner equipped with small groups of slots arranged close together and/or rows of holes, aligned transversely, with the relative pilot holes at the ends. The burner body has a polygonal cross-section, in particular featuring a diffuser with two angled sides which, as shown in FIG. 2, have slots across the joint between these sides, creating a double-horned flame on a transverse plane of the diffuser itself. The flame in this burner is more stable and noise level is reduced.
However, prior art does not envisage the reduction of harmful emissions of nitrogen oxides and carbon monoxide. This may be justified by the fact it was considered impossible to solve the problem of reducing pollutant emissions from atmospheric burners simply by acting on the combustion method or on the proportioning of the burner itself.